The present invention relates to a novel anisotropically electroconductive adhesive composition or, more particularly, to an anisotropically electroconductive adhesive composition used for making electric connection between electrode terminals, for example, of an electric circuit formed on a rigid or flexible printed circuit board and various kinds of electronic devices such as liquid crystal display units.
It is a remarkable trend in recent years that various kinds of electric and electronic instruments are designed to be very compact in size and thickness and are used sometimes under adverse ambient conditions to encounter a high temperature, high humidity and vibrations or mechanical shocks as outdoors and in an automobile engine room. As a matter of course, this trend can be realized only with a substantial improvement in the reliability of electric connection between electrode terminals on various kinds of electronic devices and electric circuits. While it is conventional that such an electric connection is made by using an anisotropically electroconductive adhesive composition consisting of an insulating adhesive resin as a matrix and fine particles having electric conductivity compounded in an appropriate amount with and dispersed in the matrix of the adhesive resin, the above mentioned requirement for higher and higher reliability of the anisotropic electric connection can be achieved by using special high-grade conductive particles which are particles of a metal such as nickel or a plastic resin having particle size distribution as uniform as possible and provided with a plating layer of a noble metal such as gold to exhibit a relatively low contact resistance.
Needless to say, electroconductive powders consisting of particles having a plating layer of a noble metal are very expensive. When the powder is made from a metal such as nickel, in particular, the particles naturally have a density much larger than that of the insulating adhesive resin as the matrix so that a trouble to decrease the workability in preparation is sometimes caused that segregation takes place between the metallic particles and the adhesive resin due to the large difference in the densities.